Internet Engineering Task Force (IETF) Y. Lee, Ed.
Request for Comments: 7446 Huawei
Category: Informational G. Bernstein, Ed.
ISSN: 2070-1721 Grotto Networking
D. Li
Huawei
W. Imajuku
NTT
February 2015
Routing and Wavelength Assignment Information Modelfor Wavelength Switched Optical Networks
Abstract
This document provides a model of information needed by the Routing
and Wavelength Assignment (RWA) process in Wavelength Switched
Optical Networks (WSONs). The purpose of the information described
in this model is to facilitate constrained optical path computation
in WSONs. This model takes into account compatibility constraints
between WSON signal attributes and network elements but does not
include constraints due to optical impairments. Aspects of this
information that may be of use to other technologies utilizing a
GMPLS control plane are discussed.
Status of This Memo
This document is not an Internet Standards Track specification; it is
published for informational purposes.
This document is a product of the Internet Engineering Task Force
(IETF). It represents the consensus of the IETF community. It has
received public review and has been approved for publication by the
Internet Engineering Steering Group (IESG). Not all documents
approved by the IESG are a candidate for any level of Internet
Standard; see Section 2 of RFC 5741.
Information about the current status of this document, any errata,
and how to provide feedback on it may be obtained at
http://www.rfc-editor.org/info/rfc7446.
Lee, et al. Informational [Page 1]

RFC 7446 WSON Information Model February 20151. Introduction
The purpose of the WSON information model described in this document
is to facilitate constrained optical path computation, and as such it
is not a general-purpose network management information model. This
constraint is frequently referred to as the "wavelength continuity"
constraint, and the corresponding constrained optical path
computation is known as the Routing and Wavelength Assignment (RWA)
problem. Hence, the information model must provide sufficient
topology and wavelength restriction and availability information to
support this computation. More details on the RWA process and WSON
subsystems and their properties can be found in [RFC6163]. The model
defined here includes constraints between WSON signal attributes and
network elements but does not include optical impairments.
In addition to presenting an information model suitable for path
computation in WSON, this document also highlights model aspects that
may have general applicability to other technologies utilizing a
GMPLS control plane. The portion of the information model applicable
to technologies beyond WSON is referred to as "general" to
distinguish it from the "WSON-specific" portion that is applicable
only to WSON technology.
2. Terminology
Refer to [RFC6163] for definitions of Reconfigurable Optical Add/Drop
Multiplexer (ROADM), RWA, Wavelength Conversion, Wavelength Division
Multiplexing (WDM), WSON, and other related terminology used in this
document.
3. Routing and Wavelength Assignment Information Model
The WSON RWA information model in this document comprises four
categories of information. The categories are independent of whether
the information comes from a switching subsystem or from a line
subsystem -- a switching subsystem refers to WSON nodes such as a
ROADM or an Optical Add/Drop Multiplexer (OADM), and a line subsystem
refers to devices such as WDM or Optical Amplifier. The categories
are these:
o Node Information
o Link Information
o Dynamic Node Information
o Dynamic Link Information
Lee, et al. Informational [Page 3]

RFC 7446 WSON Information Model February 2015
Note that this is roughly the categorization used in Section 7 of
[G.7715].
In the following, where applicable, the Reduced Backus-Naur Form
(RBNF) syntax of [RBNF] is used to aid in defining the RWA
information model.
3.1. Dynamic and Relatively Static Information
All the RWA information of concern in a WSON network is subject to
change over time. Equipment can be upgraded; links may be placed in
or out of service and the like. However, from the point of view of
RWA computations, there is a difference between information that can
change with each successive connection establishment in the network
and information that is relatively static and independent of
connection establishment. A key example of the former is link
wavelength usage since this can change with connection setup/teardown
and this information is a key input to the RWA process. Examples of
relatively static information are the potential port connectivity of
a WDM ROADM, and the channel spacing on a WDM link.
This document separates, where possible, dynamic and static
information so that these can be kept separate in possible encodings.
This allows for separate updates of these two types of information,
thereby reducing processing and traffic load caused by the timely
distribution of the more dynamic RWA WSON information.
4. Node Information (General)
The node information described here contains the relatively static
information related to a WSON node. This includes connectivity
constraints amongst ports and wavelengths since WSON switches can
exhibit asymmetric switching properties. Additional information
could include properties of wavelength converters in the node, if any
are present. In [Switch] it was shown that the wavelength
connectivity constraints for a large class of practical WSON devices
can be modeled via switched and fixed connectivity matrices along
with corresponding switched and fixed port constraints. These
connectivity matrices are included with the node information, while
the switched and fixed port wavelength constraints are included with
the link information.
Formally,
<Node_Information> ::= <Node_ID> [<ConnectivityMatrix>...]
Where the Node_ID would be an appropriate identifier for the node
within the WSON RWA context.
Lee, et al. Informational [Page 4]

RFC 7446 WSON Information Model February 2015
Note that multiple connectivity matrices are allowed and hence can
fully support the most-general cases enumerated in [Switch].
4.1. Connectivity Matrix
The connectivity matrix (ConnectivityMatrix) represents either the
potential connectivity matrix for asymmetric switches (e.g., ROADMs
and such) or fixed connectivity for an asymmetric device such as a
multiplexer. Note that this matrix does not represent any particular
internal blocking behavior but indicates which input ports and
wavelengths could possibly be connected to a particular output port.
For a switch or ROADM, representing blocking that is dependent on the
internal state is beyond the scope of this document. Due to its
highly implementation-dependent nature, it would most likely not be
subject to standardization in the future. The connectivity matrix is
a conceptual M by N matrix representing the potential switched or
fixed connectivity, where M represents the number of input ports and
N the number of output ports. This is a "conceptual" matrix since
the matrix tends to exhibit structure that allows for very compact
representations that are useful for both transmission and path
computation.
Note that the connectivity matrix information element can be useful
in any technology context where asymmetric switches are utilized.
<ConnectivityMatrix> ::= <MatrixID>
<ConnType>
<Matrix>
Where
<MatrixID> is a unique identifier for the matrix.
<ConnType> can be either 0 or 1 depending upon whether the
connectivity is either fixed or switched.
<Matrix> represents the fixed or switched connectivity in that
Matrix(i, j) = 0 or 1 depending on whether input port i can connect
to output port j for one or more wavelengths.
5. Node Information (WSON Specific)
As discussed in [RFC6163], a WSON node may contain electro-optical
subsystems such as regenerators, wavelength converters or entire
switching subsystems. The model present here can be used in
characterizing the accessibility and availability of limited
Lee, et al. Informational [Page 5]

RFC 7446 WSON Information Model February 2015
resources such as regenerators or wavelength converters as well as
WSON signal attribute constraints of electro-optical subsystems. As
such, this information element is fairly specific to WSON
technologies.
In this document, the term "resource" is used to refer to a physical
component of a WSON node such as a regenerator or a wavelength
converter. Multiple instances of such components are often present
within a single WSON node. This term is not to be confused with the
concept of forwarding or switching resources such as bandwidth or
lambdas.
A WSON node may include regenerators or wavelength converters
arranged in a shared pool. As discussed in [RFC6163], a WSON node
can also include WDM switches that use optical-electronic-optical
(OEO) processing. There are a number of different approaches used in
the design of WDM switches containing regenerator or converter pools.
However, from the point of view of path computation, the following
need to be known:
1. The nodes that support regeneration or wavelength conversion.
2. The accessibility and availability of a wavelength converter to
convert from a given input wavelength on a particular input port
to a desired output wavelength on a particular output port.
3. Limitations on the types of signals that can be converted and the
conversions that can be performed.
Since resources tend to be packaged together in blocks of similar
devices, e.g., on line cards or other types of modules, the
fundamental unit of identifiable resource in this document is the
"resource block".
A resource block is a collection of resources from the same WSON node
that are grouped together for administrative reasons and for ease of
encoding in the protocols. All resources in the same resource block
behave in the same way and have similar characteristics relevant to
the optical system, e.g., processing properties, accessibility, etc.
A resource pool is a collection of resource blocks for the purpose of
representing throughput or cross-connect capabilities in a WSON node.
A resource pool associates input ports or links on the node with
output ports or links and is used to indicate how signals may be
passed from an input port or link to an output port or link by way of
a resource block (in other words, by way of a resource). A resource
pool may, therefore, be modeled as a matrix.
Lee, et al. Informational [Page 6]

RFC 7446 WSON Information Model February 2015
A resource block may be present in multiple resource pools.
This leads to the following formal high-level model:
<Node_Information> ::= <Node_ID>
[<ConnectivityMatrix>...]
[<ResourcePool>]
Where
<ResourcePool> ::= <ResourceBlockInfo>...
[<ResourceAccessibility>...]
[<ResourceWaveConstraints>...]
[<RBPoolState>]
First, the accessibility of resource blocks is addressed; then, their
properties are discussed.
5.1. Resource Accessibility/Availability
A similar technique as used to model ROADMs, and optical switches can
be used to model regenerator/converter accessibility. This technique
was generally discussed in [RFC6163] and consisted of a matrix to
indicate possible connectivity along with wavelength constraints for
links/ports. Since regenerators or wavelength converters may be
considered a scarce resource, it is desirable that the model include,
if desired, the usage state (availability) of individual regenerators
or converters in the pool. Models that incorporate more state to
further reveal blocking conditions on input or output to particular
converters are for further study and not included here.
The three-stage model is shown schematically in Figures 1 and 2. The
difference between the two figures is that in Figure 1 it's assumed
that each signal that can get to a resource block may do so, while in
Figure 2 the access to sets of resource blocks is via a shared fiber
that imposes its own wavelength collision constraint. Figure 1 shows
that there can be more than one input to each resource block since
each input represents a single wavelength signal, while Figure 2
shows a single WDM input or output, e.g., a fiber, to/from each set
of blocks.
Lee, et al. Informational [Page 7]

RFC 7446 WSON Information Model February 2015
This model assumes N input ports (fibers), P resource blocks
containing one or more identical resources (e.g., wavelength
converters), and M output ports (fibers). Since not all input ports
can necessarily reach each resource block, the model starts with a
resource pool input matrix RI(i,p) = {0,1} depending on whether input
port i can potentially reach resource block p.
Since not all wavelengths can necessarily reach all the resources or
the resources may have limited input wavelength range, the model has
a set of relatively static input port constraints for each resource.
In addition, if the access to a set of resource blocks is via a
shared fiber (Figure 2), this would impose a dynamic wavelength
availability constraint on that shared fiber. The resource block
input port constraint is modeled via a static wavelength set
mechanism, and the case of shared access to a set of blocks is
modeled via a dynamic wavelength set mechanism.
Next, a state vector RA(j) = {0,...,k} is used to track the number of
resources in resource block j in use. This is the only state kept in
the resource pool model. This state is not necessary for modeling
"fixed" transponder system or full OEO switches with WDM interfaces,
i.e., systems where there is no sharing.
After that, a set of static resource output wavelength constraints
and possibly dynamic shared output fiber constraints maybe used. The
static constraints indicate what wavelengths a particular resource
block can generate or is restricted to generating, e.g., a fixed
regenerator would be limited to a single lambda. The dynamic
constraints would be used in the case where a single shared fiber is
used to output the resource block (Figure 2).
Finally, to complete the model, a resource pool output matrix RE(p,k)
= {0,1} depending on whether the output from resource block p can
reach output port k, may be used.
Lee, et al. Informational [Page 8]

RFC 7446 WSON Information Model February 2015
<RBPoolState> ::= <ResourceBlockID>
<NumResourcesInUse>
[<RBSharedAccessWaveAvailability>]
[<RBPoolState>]
Note that, except for <RBPoolState>, all the components of
<ResourcePool> are relatively static. Also, the
<InAvailableWavelengths> and <OutAvailableWavelengths> are only used
in the cases of shared input or output access to the particular
block. See the resource block information in the next section for
how this is specified.
5.2. Resource Signal Constraints and Processing Capabilities
The wavelength conversion abilities of a resource (e.g., regenerator,
wavelength converter) were modeled in the <OutputWaveConstraints>
previously discussed. As discussed in [RFC6163], the constraints on
an electro-optical resource can be modeled in terms of input
constraints, processing capabilities, and output constraints:
<ResourceBlockInfo> ::= <ResourceBlockSet>
[<InputConstraints>]
[<ProcessingCapabilities>]
[<OutputConstraints>]
Where <ResourceBlockSet> is a list of resource block identifiers
with the same characteristics. If this set is missing, the
constraints are applied to the entire network element.
The <InputConstraints> are constraints are based on signal
compatibility and/or shared access constraint indication. The
details of these constraints are defined in Section 5.3.
<InputConstraints> ::= <SharedInput>
[<OpticalInterfaceClassList>]
[<ClientSignalList>]
The <ProcessingCapabilities> are important operations that the
resource (or network element) can perform on the signal. The details
of these capabilities are defined in Section 5.3.
Lee, et al. Informational [Page 11]

RFC 7446 WSON Information Model February 2015
<ProcessingCapabilities> ::= [<NumResources>]
[<RegenerationCapabilities>]
[<FaultPerfMon>]
[<VendorSpecific>]
The <OutputConstraints> are either restrictions on the properties of
the signal leaving the block, options concerning the signal
properties when leaving the resource, or shared fiber output
constraint indication.
<OutputConstraints> := <SharedOutput>
[<OpticalInterfaceClassList>]
[<ClientSignalList>]
5.3. Compatibility and Capability Details5.3.1. Shared Input or Output Indication
As discussed in Section 5.2 and shown in Figure 2, the input or
output access to a resource block may be via a shared fiber. The
<SharedInput> and <SharedOutput> elements are indicators for this
condition with respect to the block being described.
5.3.2. Optical Interface Class List
<OpticalInterfaceClassList> ::= <OpticalInterfaceClass> ...
The Optical Interface Class is a unique number that identifies all
information related to optical characteristics of a physical
interface. The class may include other optical parameters related to
other interface properties. A class always includes signal
compatibility information.
The content of each class is out of the scope of this document and
can be defined by other entities (e.g., the ITU, optical equipment
vendors, etc.).
Since even current implementation of physical interfaces may support
different optical characteristics, a single interface may support
multiple interface classes. Which optical interface class is used
among all the ones available for an interface is out of the scope of
this document but is an output of the RWA process.
Lee, et al. Informational [Page 12]

RFC 7446 WSON Information Model February 20155.3.3. Acceptable Client Signal List
The list is simply:
<ClientSignalList>::=[<G-PID>]...
Where the Generalized Protocol Identifiers (G-PID) object represents
one of the IETF-standardized G-PID values as defined in [RFC3471] and
[RFC4328].
5.3.4. Processing Capability List
The ProcessingCapabilities are defined in Section 5.2.
The processing capability list sub-TLV is a list of processing
functions that the WSON network element (NE) can perform on the
signal including:
1. number of resources within the block
2. regeneration capability
3. fault and performance monitoring
4. vendor-specific capability
Note that the code points for fault and performance monitoring and
vendor-specific capability are subject to further study.
6. Link Information (General)
MPLS-TE routing protocol extensions for OSPF [RFC3630] and IS-IS
[RFC5305], along with GMPLS routing protocol extensions for OSPF
[RFC4203] and IS-IS [RFC5307] provide the bulk of the relatively
static link information needed by the RWA process. However, WSONs
bring in additional link-related constraints. These stem from
characterizing WDM line systems, restricting laser transmitter
tuning, and switching subsystem port wavelength constraints, e.g.,
"colored" ROADM drop ports.
The following syntax summarizes both information from existing GMPLS
routing protocols and new information that may be needed by the RWA
process.
Lee, et al. Informational [Page 13]

RFC 7446 WSON Information Model February 2015
<LinkInfo> ::= <LinkID>
[<AdministrativeGroup>]
[<InterfaceCapDesc>]
[<Protection>]
[<SRLG>...]
[<TrafficEngineeringMetric>]
[<PortLabelRestriction>...]
Note that these additional link characteristics only apply to line-
side ports of a WDM system or add/drop ports pertaining to the
resource pool (e.g., regenerator or wavelength converter pool). The
advertisement of input/output tributary ports is not intended here.
6.1. Administrative Group
Administrative Group: Defined in [RFC3630] and extended for MPLS-TE
[RFC7308]. Each set bit corresponds to one administrative group
assigned to the interface. A link may belong to multiple groups.
This is a configured quantity and can be used to influence routing
decisions.
6.2. Interface Switching Capability Descriptor
InterfaceSwCapDesc: Defined in [RFC4202]; lets us know the different
switching capabilities on this GMPLS interface. In both [RFC4203]
and [RFC5307], this information gets combined with the maximum Link
State Protocol Data Unit (LSP) bandwidth that can be used on this
link at eight different priority levels.
6.3. Link Protection Type (for This Link)
Protection: Defined in [RFC4202] and implemented in [RFC4203] and
[RFC5307]. Used to indicate what protection, if any, is guarding
this link.
6.4. Shared Risk Link Group Information
SRLG: Defined in [RFC4202] and implemented in [RFC4203] and
[RFC5307]. This allows for the grouping of links into shared risk
groups, i.e., those links that are likely, for some reason, to fail
at the same time.
Lee, et al. Informational [Page 14]

RFC 7446 WSON Information Model February 20156.5. Traffic Engineering Metric
TrafficEngineeringMetric: Defined in [RFC3630] and [RFC5305]. This
allows for the identification of a data-channel link metric value for
traffic engineering that is separate from the metric used for path
cost computation of the control plane.
Note that multiple "link metric values" could find use in optical
networks; however, it would be more useful to the RWA process to
assign these specific meanings such as "link mile" metric,
"probability of failure" metric, etc.
6.6. Port Label Restrictions
Port label restrictions could be applied generally to any label types
in GMPLS by adding new kinds of restrictions. Wavelength is a type
of label.
Port label (wavelength) restrictions (PortLabelRestriction) model the
label (wavelength) restrictions that the link and various optical
devices, such as Optical Cross-Connects (OXCs), ROADMs, and waveband
multiplexers, may impose on a port. These restrictions tell us what
wavelength may or may not be used on a link and are relatively
static. This plays an important role in fully characterizing a WSON
switching device [Switch]. Port wavelength restrictions are
specified relative to the port in general or to a specific
connectivity matrix (Section 4.1). [Switch] gives an example where
both switch and fixed connectivity matrices are used and both types
of constraints occur on the same port.
<PortLabelRestriction> ::= <MatrixID>
<RestrictionType>
<Restriction parameters list>
<Restriction parameters list> ::=
<Simple label restriction parameters> |
<Channel count restriction parameters> |
<Label range restriction parameters> |
<Simple+channel restriction parameters> |
<Exclusive label restriction parameters>
Lee, et al. Informational [Page 15]

RFC 7446 WSON Information Model February 2015
<Simple label restriction parameters> ::= <LabelSet> ...
<Channel count restriction parameters> ::= <MaxNumChannels>
<Label range restriction parameters> ::= <MaxLabelRange>
(<LabelSet> ...)
<Simple+channel restriction parameters> ::= <MaxNumChannels>
(<LabelSet> ...)
<Exclusive label restriction parameters> ::= <LabelSet> ...
Where
MatrixID is the ID of the corresponding connectivity matrix (Section4.1).
The RestrictionType parameter is used to specify general port
restrictions and matrix-specific restrictions. It can take the
following values and meanings:
SIMPLE_LABEL: Simple label (wavelength) set restriction; the
LabelSet parameter is required.
CHANNEL_COUNT: The number of channels is restricted to be less
than or equal to the MaxNumChannels parameter (which is
required).
LABEL_RANGE: Used to indicate a restriction on a range of labels
that can be switched. For example, a waveband device with a
tunable center frequency and passband. This constraint is
characterized by the MaxLabelRange parameter, which indicates
the maximum range of the labels, e.g., which may represent a
waveband in terms of channels. Note that an additional
parameter can be used to indicate the overall tuning range.
Specific center frequency tuning information can be obtained
from information about the dynamic channel in use. It is
assumed that both center frequency and bandwidth (Q) tuning can
be done without causing faults in existing signals.
Lee, et al. Informational [Page 16]

RFC 7446 WSON Information Model February 2015
SIMPLE LABEL and CHANNEL COUNT: In this case, the accompanying
label set and MaxNumChannels indicate labels permitted on the
port and the maximum number of labels that can be
simultaneously used on the port.
LINK LABEL_EXCLUSIVITY: A label (wavelength) can be used at most
once among a given set of ports. The set of ports is specified
as a parameter to this constraint.
Restriction-specific parameters are used with one or more of the
previously listed restriction types. The currently defined
parameters are:
LabelSet is a conceptual set of labels (wavelengths).
MaxNumChannels is the maximum number of channels that can be
simultaneously used (relative to either a port or a matrix).
LinkSet is a conceptual set of ports.
MaxLabelRange indicates the maximum range of the labels. For
example, if the port is a "colored" drop port of a ROADM, then there
are two restrictions: (a) CHANNEL_COUNT, with MaxNumChannels = 1, and
(b) SIMPLE_WAVELENGTH, with the wavelength set consisting of a single
member corresponding to the frequency of the permitted wavelength.
See [Switch] for a complete waveband example.
This information model for port wavelength (label) restrictions is
fairly general in that it can be applied to ports that have label
restrictions only or to ports that are part of an asymmetric switch
and have label restrictions. In addition, the types of label
restrictions that can be supported are extensible.
6.6.1. Port-Wavelength Exclusivity Example
Although there can be many different ROADM or switch architectures
that can lead to the constraint where a lambda (label) maybe used at
most once on a set of ports, Figure 3 shows a ROADM architecture
based on components known as Wavelength Selective Switches (WSSes)
[OFC08]. This ROADM is composed of splitters, combiners, and WSSes.
This ROADM has 11 output ports, which are numbered in the diagram.
Output ports 1-8 are known as drop ports and are intended to support
a single wavelength. Drop ports 1-4 output from WSS 2, which is fed
from WSS 1 via a single fiber. Due to this internal structure, a
constraint is placed on the output ports 1-4 that a lambda can be
used only once over the group of ports (assuming unicast and not
multicast operation). The output ports 5-8 have a similar constraint
due to the internal structure.
Lee, et al. Informational [Page 17]

RFC 7446 WSON Information Model February 20157.1. Dynamic Link Information (General)
For WSON links, the wavelength availability and which wavelengths are
in use for shared backup purposes can be considered dynamic
information and hence are grouped with the dynamic information in the
following set:
<DynamicLinkInfo> ::= <LinkID>
<AvailableLabels>
[<SharedBackupLabels>]
AvailableLabels is a set of labels (wavelengths) currently available
on the link. Given this information and the port wavelength
restrictions, one can also determine which wavelengths are currently
in use. This parameter could potentially be used with other
technologies that GMPLS currently covers or may cover in the future.
SharedBackupLabels is a set of labels (wavelengths) currently used
for shared backup protection on the link. An example usage of this
information in a WSON setting is given in [Shared]. This parameter
could potentially be used with other technologies that GMPLS
currently covers or may cover in the future.
Note that the above does not dictate a particular encoding or
placement for available label information. In some routing
protocols, it may be advantageous or required to place this
information within another information element such as the Interface
Switching Capability Descriptor (ISCD). Consult the extensions that
are specific to each routing protocol for details of placement of
information elements.
7.2. Dynamic Node Information (WSON Specific)
Currently the only node information that can be considered dynamic is
the resource pool state, and it can be isolated into a dynamic node
information element as follows:
<DynamicNodeInfo> ::= <NodeID> [<ResourcePool>]
8. Security Considerations
This document discusses an information model for RWA computation in
WSONs. From a security standpoint, such a model is very similar to
the information that can be currently conveyed via GMPLS routing
protocols. Such information includes network topology, link state
and current utilization, as well as the capabilities of switches and
Lee, et al. Informational [Page 19]